1. Field of the Invention
This invention relates to an electric discharge machining (EDM) machine for fine holes and an EDM method for fine holes using such machine to process a workpiece by a fine hole machining electrode.
2. Description of the Related Art
In conventional EDM machines for fine holes using a fine solid electrode or tubular electrode, an attempt has been made to decrease deflection of a leading end of the electrode thereby to achieve precise fine hole machining.
A guide for conducting the precise fine hole machining is shown by an intermediate electrode guide mentioned in Japanese Laid Open Patent Publication No. 60-108234, a grease guide mentioned in Japanese Laid Open Patent Publication No. 1-164526, or a bearing guide mentioned in Japanese Laid Open Patent Publication No. 07-285030.
In addition, a method to decrease distortion of the machining electrode by a working fluid is exemplified by a method mentioned in Japanese Laid Open Patent Publication No. 61-76219 in which a thickener is added.
However, in these fine hole EDM machines, the machining electrodes have low rigidity since their diameter .phi. is not more than 0.3 mm, especially not more than 0.1 mm. Therefore, there are some problems as mentioned below when such solid or hollow electrode is used. That is, even if the intermediate guide mentioned in the publication No. 60-108234 or the like is adopted, it may be difficult to insert the electrode into the fine hole electrode guide. Moreover, it may be difficult to insert the electrode into the intermediate electrode guide or the like for reducing deflection of the electrode tip end.
When the rigidity of the electrode is not sufficient in machining, the electrode is distorted between an electrode holder and the intermediate guide or between the intermediate guide and the electrode guide in feeding the electrode, even if the intermediate guide is provided. In this case, it is hard to feed the electrode as much as required in machining. Consequently, there take place problems that a machining speed becomes slow, that a machining depth limit becomes shallow, and that a machining time increases thereby to deteriorate machining hole accuracy.
In the method of adding the thickener as in the publication No. 61-76219, a machined hole is used as a guide. Thus, it cannot solve the above problems such as the difficulty of inserting electrode into the electrode guide or the intermediate guide.